This invention relates generally as indicated to a process and jig for field forming relatively large diameter plastic pipe or conduit. The invention of this application represents certain improvements in plastic pipe bending jigs of the type shown in applicants' prior U.S. Pat. No. 3,776,539 issued Dec. 4, 1973.
In applicants' above noted prior patent, there is illustrated several forms of a plastic pipe bending jig, at least one of which has proven useful in the field forming of relatively small diameter plastic pipe or tube. Since plastic pipe must be heated to be bent, and since heated plastic pipe is generally like wet spaghetti, it is important that the pipe or tube, particularly when of a larger diameter, be placed and maintained on a substantially flat and dry surface. Even the slightest irregularity can cause an undesired deformation in the pipe or tube to be bent. For large size conduit in the range of from about 2 to about 6 inches in diameter, such conduit, especially when heated, is difficult to support, carry or transport. It is thus easier to provide a jig which includes guides which may be positioned over the pipe. It is accordingly important that the jig be of light weight and yet sturdy construction. Moreover, it should be readily capable of being assembled in the field, and when assembled readily adjustable to form the desired bend in the particular size conduit involved.
The jig of the present invention provides a two-piece spreader tube and a right and left hand linear guide, each guide being adjustable in width. The angle of the guide and the spacing of such guides on the spreader tube is readily determinable and capable of selection. Each guide is readily adjustable in width to accommodate the conduit diameters noted above and each guide is provided with a protractor readily clamped to the spreader tube, the protractor of one guide including an offset scale so that offsets or curves with generally parallel tangents may be formed. The spreader tube includes a scale to ascertain the chord of the curve in terms of the radius for given degrees of bend.
The spreader tube may be disassembled and the guides disassembled from the spreader tube so that the components of the bending jig may be placed in a compact fashion as a kit in a carrying box.
It is a principal object of the present invention to provide a jig for the field bending of relatively large diameter plastic conduit which may be assembled and disassembled to form a readily transportable and lightweight kit.
Another principal object is the provision of a field kit for the formation of bends in plastic pipe which includes two linear guides mounted beneath a spreader bar with the width of the guides being readily adjustable through a substantial range.
Another important object is the provision of such jig for bending relatively large diameter plastic pipe wherein the guides are pivoted each to a protractor in turn clamped to the spreader tube so that the angular inclination of the guide with respect to the tube may readily be set.
Yet another important object is the provision of such jig wherein the spreader tube includes a scale by which the spacing of the guides may be obtained, such scale setting the chord of the bend in terms of the radius for certain given degrees of bend.
Another object is the provision of a lightweight easily assembled jig for the field bending of plastic pipe.
Still another object is the provision of a method for field forming bends in plastic pipe which includes the steps of placing first one set linear guide over the pipe and then the other after the pipe is brought to the desired degree of curvature on a flat surface.
Other objects and advantages of the present invention will become apparent as the following description proceeds.
To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.